Sports Medicine Research: In the Lab & In the Field: Diffusion Tensor Imaging of Sports-Related Concussion (Sports Med Res)
Monday, February 4, 2013

Diffusion Tensor Imaging of Sports-Related Concussion

Diffusion tensor imaging of sports-related concussion in adolescents

Virji-Babul N., Borich MR., Makan N., Moore T., Frew K., Emery CA., Boyd LA. Pediatric Neurology. 2013; 48: 24-29.

The impact that a concussion has on an immature adolescent brain is largely unknown. Magnetic resonance imaging advancements such as diffusion tensor imaging may help us understand these changes because it provides quantitative measure of the subtle changes within the white matter tissue in the brain following a concussion. Therefore, the purpose of this study was to use diffusion tensor imaging to investigate the short-term structural differences between 12 adolescents that had sustained a recent concussion (within 2 months) and 10 adolescent athletes with no concussion history. Additionally, the association of diffusion tensor imaging measures and the Sports Concussion Assessment Tool 2 (SCAT2) was assessed. The authors found that the integrity of the white matter  differed between the concussed and non-concussed groups.  Furthermore, the SCAT2 was associated with two measures of white matter integrity.  However, there was no difference in SCAT2 scores between groups.

A concussion is defined as a pathophysiological process that is induced by traumatic biomechanical forces. Thus, when a neuron is stretched many cellular changes take place (known as the neurometabolic cascade; Hovda & Giza). These changes are very subtle and most imaging techniques cannot detect them.  These researchers provide preliminary evidence that brains exposed to a recent concussion have differences in the integrity of the white matter compared to healthy brains that can be observed with diffusion tensor imaging. The observed changes in the white matter may be caused by mechanical forces from the concussion that stretch neurons in the white matter and cause ion channels to open. This could lead to an increase in intracellular water and decrease in extracellular water, which may be one reason there is decreased diffusivity. These observed changes could also be associated with the tissue injury itself that induces inflammation.  There are several limitations to this study that should be noted. Firstly, the sample size is small, which limits our ability to apply these results to our clinical populations. In addition, there were a varying number of concussions (from 1 to 4 concussions) within the concussed group. Also, there was a varying time for the concussed group to get there diffusion tensor imaging (up to 2 months post injury). These variables could have altered the outcome of their data. This preliminary research will hopefully inspire future research to determine if diffusion tensor imaging has a role in diagnosing concussions, monitoring recovery, and return-to-play decisions. Do you think magnetic resonance imaging, like diffusion tensor imaging, would be a helpful diagnostic tool for concussions?

Written by: Jane McDevitt MS, ATC, CSCS
Reviewed by: Jeffrey Driban

Related Posts:
Virji-Babul N, Borich MR, Makan N, Moore T, Frew K, Emery CA, & Boyd LA (2013). Diffusion tensor imaging of sports-related concussion in adolescents. Pediatric Neurology, 48 (1), 24-9 PMID: 23290016

2 comments:

Greg said...

I think this is a great study and it is always exciting to see new research, especially as it pertains to concussions, that may allow us to have a quantitative picture of the injury. Part of me is curious though as to whether or not DTI may be a bit too sensitive in certain cases. For instance, if you think of it like bone bruises on an MRI. 1. You don't "treat" the bone bruise outside pain 2. Even after the bone bruise has become completely asymptomatic you can still visualize it on MRI. That said, I don't know if it helps our diagnosis being that we don't really have a way (that I know of) to treat "decreased diffusivity" and it may be a case where we are able to see changes that don't have much clinical relevance. I do think it is important that they paired the test with the SCAT2 as this does help somewhat to correlate the two. From my perspective though, I don't do think that as many of our issues stem around the true diagnosis of concussions but rather the return to play. Again, I think research like this is extremely interesting and very important but I am not sure how applicable it is in terms of determining when someone is truly safe to return to participation. What are your thoughts?

Jane McDevitt said...

Greg,

I agree this research is far from ready to be applied to the concussion evaluation. It is expensive and DTI is very difficult to read. However, the research behind it is important because DTI can detect the subtle changes the occur in the brain. This will at least answer more questions related to the physiology of the injury. I also agree that the SCAT2 was not correlated to the DTI very well. I thought it was curious that the SCAT2 scores between the 2 groups were not even significantly different, which makes me question the sensitivity and specificity of this tool. I think these types of imaging studies it are importnat to focus on how long the brain takes to heal. This study specifically had some limitations because concussed athletes sometimes didn't get the imaging done up to 2 months and the sample size was small. Though, even with these limitations there were structural differences between the concussed brains and non-concussed brains. I feel that is important to note because if the concussion assessment tools cant detect these structural differences that can last for up to 2 months than we need to develop better assessments. I also agree that specific diagnosis of the concussion injury is not as important as safe return to play. We need to know when the athlete is back to baseline to being the RTP process so again what if there are still structural deficits in the brain that are not picked up by the tests we are currently using. This leads to sending back some athletes before they should. My thoughts on this type of research is that we need to continue with this research to create a "gold standard" test that has high sensitivity and specificity to diagnose concussion. Just like the "gold standard" for ACL diagnosis is arthroscopy. Once we get a "gold standard" we can compare concussion tests (new and old) to it and create better tests that can detect concussion s/s so we can follow the deficits and return an athlete to play safely.

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